Induction disk for watthour meters and the like



Nov. 14, 1950 J. PRINCE EI'AL 2,529,571

INDUCTION DISK FOR WATTHOUR METERS AND THE LIKE Filed Oct. 15, 1945 By INVENTORS ATTORNEY Patented Nov. 14, 1950 INDUCTION DISK FOR WATTHOUR METERS AND THE LIKE John Prince and Maurice Whitehead, Hollinwood, England Application October 15, 1945, Serial No. 622,420 In Great Britain October 21, 1944 14 Claims. 1

This invention relates to induction discs for watthour meters and the like, such as motors employing induction discs for eddy current brakes, and other induction disc apparatus.

It is important in an induction disc, especially for meter use, to have in the rotor disc, considered as a whole, as high a ratio of conductivity to mass as is possible. At present, it is general practice to make the disc of aluminum and of uniform thickness, since this metal represents the best economic compromise between high conductivity and low density.

Rotor discs for electric meters and like induction motor movements have been proposed in United States Patent No. 1,913,260, having a centre portion of insulating material, or of metal having comparatively high electrical resistance, with the object of overcoming adverse interaction between eddy currents from different areas of generation, which would otherwise be liable to circulate across the diameter and within the centre portion. At the same time certain other advantages from the said construction, such as being of lighter weight, were contemplated and the manner of its attainment was described as attributable to the inclusion of air or other insulating medium. The construction, however, except for certain purposes where the avoidance of interaction as aforesaid is of major importance, has, the definite disadvantage arising from the use of insulating material or high resistance metal for the centre portion of the disc that the current path therethrough is either cut off or; is of high resistance.

The present invention is based on an appreciation that there are many electrical conductors having a high conductivity/mass ratio but which are chemically unstable, and therefore have not as yet been used for induction discs.

The object of the present invention is to enable such other electrical conductors to be used for the construction of industion discs, thus making available the inherent characteristics of such material.

According to the present invention, the improved induction disc or any part thereof comprises a material of high conductivity/mass ratio, but which is chemically unstable, and a protective sheath therefor of stable material.

In one example of the invention, the disc comprises chemically unstable electrically conductive material such as lithium or sodium. The protective sheath may comprise an extremely thin coating of a metallic or non-metallic material such as aluminium, or any other available and suitable substance.

The protective sheath may be formed by any efiective process including spinning, welding, electro-deposition or spraying.

The disc may be sectional, for example as described in applicants copending application, Serial No. 622,756, filed October 17, 1945, now abandoned, which sectionalisation makes possible various combinations in which any part of the disc may be of a material which is chemically unstable with a protective sheath, Whilst the other part or parts is or are chemically stable.

In the accompanying drawing:

Fig. 1 is a cross-sectional elevation of half an induction disc made in accordance with one example of the invention,

Fig. 2 is a part plan of the disc shown in Fig.1,

Figs. 37 show alternative or modified forms of the invention.

In the example shown in Figs. 1 and 2 of the drawings an annular disheshaped portion of shallow channel cross section, having a base a and walls a a manufactured from aluminium 0.025 cm. thick, 0.100 cm. overall depth and 8.5 cms. diameter, contains metallic sodium b. A

circular disc 0 of aluminium 0.025 cm. thick, 8.5

, bedded.

In a further example, the envelope is manufactured of glass.

In order to ensure that the high conductivity/low density metal is homogeneous and completely fills the envelope, the filling process may be carried out by any of the following methods. The required quantity of metal is placed in the dish-shaped portion of the disc and pressure applied, whereupon the metal fiows to the shape of the container; or the metal may be melted and poured, after which it is allowed to solidify; or the required quantity of metal is placed in the compartment and melted; or it is deposited by electrolysis; or the metal is heated in a separate container to a temperature in excess of its boiling point and is distilled into the compartment, which is maintained at a low temperature. Afterwards the remaining part c of the disc is fitted, and the compartment sealed. When employing aluminium for the envelope, the sealing may be effected by welding, soldering, or

cementing. When glass is used, the joints may be sealed by fusing or cementing.

In order to minimise chemical changes, the above processes should, where practicable, be carried out under vacuum conditions.

The metal used inside the envelope may, alternatively be lithium or any other metal with similar characteristics as regards mass, conductivity and melting point.

The ratio of conductance/mass of the rotor disc considered as a whole is thus improved, since, for example, a disc composed partly of aluminium and partly of sodium (conductivity 224x10 mhos/c. 0., density 0.971 gr. per 0. c.) is superior in this respect to one composed entirely of aluminium, (conductivity 3.115 mhos/c. c., density 2.7 gr. per c. c.).

As shown in Fig. 3, the envelope may be stepped to provide a defined outer annulus section a and extension annulus a though such extension annulus'may be omitted if not required.

In an alternative construction, as shown in Fig. 4, the disc comprises an inner disc-like section g of metal and an outer annulus section h, the latter only being of envelope form, filled with the unstable electrical conductor b and closed by a cover h The inner disc-like section g is shown integral with the metal envelope h of the outer annulus section. In Fig. 5, the outer annulus section is formed of an annular channel 2', filled with the unstable electrical conductor 1) and secured to the surface of a metal disc 7' which forms both a cover for the annular channel and the inner section of the disc. An extension 9' of the disc 7' is shown to form an extension annulus, though this may be omitted if not required.

In a further alternative construction shown in Fig. 6, and evolved from that of Fig. 5, are two channel-like sections k and k separated by an insulating ring in, of which k is secured to the metal disc 7', such sections forming separate outer annulus sections for polyphase or like use. In this case, the disc 7' may be of insulating material and the ring in may be integral therewith.

As shown in Fig. 7, the disc comprises two annular channels n and o of insulating material formed as an integral structure with a common dividing wall 10. The channels are filled with the unstable conducting metal and then sealed to the face of a disc q of insulating material. Alternatively, the channels could be formed on the face of the disc and sealed, after filling by one or two annular rings. Where separate rings are employed, they could be of metal.

The examples shown in Figs. 3 to 7 may, by suitable selection of materials as to their mass, density and conductivity for the respective inner disc-like section and outer annulus section, embody the invention of our co-pending application, Serial No. 622,756, filed October 17, 1945, except where an insulating material is used for the inner section.

Obviously many other constructional modifications are possible without departing from the nature of the invention, as, for example, by making the outer annulus section such as h of Fig. 4, non-integral with the inner disc-like section 9. The feature of the extension annulus a of Fig. 3, or of Fig. 5 may be embodied with any form of theinvention. Where defined inner and outer sections are provided, they may have a common central plane or one may be oif-set relative to the other, as may be required and as shown, for examplain Figs. '3, f1, 5 and 6. 7

What we claim is:

1. An improved induction disc comprising an inner fiat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum, and a sheath of stable material surrounding said metal.

2. An improved induction disc comprising an inner fiat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum, and a sheath of stable material surrounding said metal, said -metal being taken from the class consisting of alkali metals.

3. An improved induction disc comprising an inner flat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and taken from the class consisting of the alkali metals, and a sheath of aluminum surrounding said metal.

l. An improved induction disc comprising an inner fiat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and taken from the class consisting of the alkali metals, and a sheath of stable material surrounding said metal, said sheath being thin relative to the thickness of said metal.

5. An improved induction disc comprising an inner fiat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and taken from the class consisting of the alkali metals, and a sheath of stable material surrounding said metal, said disc being of uniform thickness.

6. An improved induction disc comprising an inner flat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and a sheath of stable material surrounding said metal, said disc being thicker at the outer area thereof than at the central portion.

'7. An improved induction disc com-prising an inner fiat annular member of a metal having a lower density than that of aluminum and which is chemically untable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and a sheath of stable material surrounding said metal, said disc being thicker at the outer area thereof than at the central portion, said metal being present in only the thicker portion of said disc.

8. An improved induction disc comprising an inner flat annular member of a metal having a lower density than that of aluminum and Which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and a sheath of stable material surrounding said metal, said disc being thicker at the outer area thereof than at the central portion, said thicker portion having an annular body of said metal.

9. An improved induction disc comprising an inner fiat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and a sheath of stable material surrounding said metal, said disc being thicker at the outer area thereof than at the central portion, said thicker portion having a plurality of annular bodies of said metal in concentric relation.

10. An improved induction disc comprising an inner flat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having a conductivity/mass ratio greater than that of aluminum and taken from the class consisting of the alkali metals and a sheath of stable material surrounding said metal, said disc being thicker at the outer area thereof than at the central portion, said thicker portion having a plurality of annular bodies of said metal in concentric relation separated by insulating material.

11. An improved induction disc comprising an inner flat annular member of a metal having a lower density than that of aluminum and which is chemically unstable when exposed to the atmosphere, said metal having conductivity/mass ratio greater than that of aluminum and taken from the class consisting of the alkali metals, and a sheath of insulating material surrounding said metal.

12. An improved induction disk comprising an inner annular member of a metal taken from the class consisting of sodium and lithium, and a sheath of a stable metal surrounding the same.

13. An improved induction disk comprising an inner annular member of a metal taken from the class consisting of sodium and lithium, and a sheath of aluminum surrounding the same.

14. An improved induction disk comprising an inner annular member of a metal taken from the class consisting of sodium and lithium, and a sheath of insulating material surrounding the same.

JOHN PRINCE. MAURICE WHITEHEAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 501,000 Duncan July 4, 1893 693,491 Brackett Feb. 18, 1902 860,961 Broido et al July 23, 1907 1,335,152 Berst Mar. 30, 1920 1,762,774 Fry June 10, 1930 1,795,498 Mathison Mar. 10, 1931 2,134,575 Pratt Oct. 25, 1938 2,328,222 McCarty Aug. 31, 1943 2,391,844 Reid Dec. 25, 1945 

